A tip type probe finds widespread applications as an element for a variety of devices by forming different types of metal films having functionality on the side surfaces thereof.
For example, by forming a metal film having a light-shielding function of shielding light having a predetermined wavelength on the top surface, a tip type probe is used as an element that generates near-field light on the top surface. Also, by forming a magnetic material or both a metal film having a light-shielding function and a magnetic material on the side surfaces, a tip type probe can be used as an element for magnetic recording or near-field light assisted magnetic recording.
A near-field light generating element is used for an optical head in an optical recording apparatus that performs high-density information recording and reproduction or an optical probe in a near-field optical microscope used for high-resolution observation. Because of the capability of handling optical information in a microscopic region exceeding the diffraction limit of light, the near-field optical technique is expected to attain high recording density and resolution unachievable with the optical technique in the related art.
A main issue of the near-field light generating element is to obtain a microscopic and strong spot of near-field light. Several shapes have been already proposed for this issue. Patent Document 1 describes the structure in which the contour shape of an optical aperture provided at the tip end of a near-field light generating element is made triangular and a polarization direction of incident light is perpendicular to one side of the triangle, so that localized strong near-field light is generated on this one side (triangular aperture method). According to Patent Documents 2 and 3 and Non-Patent Document 1, metal films are formed on two opposing surfaces among four side surfaces of a truncated square pyramid, the two surfaces have a gap not greater than the wavelength of light in the vicinity of the apex of the truncated square pyramid, and each of the metal films on the two surfaces has an apex having a curvature radius of several tens nm or less in the gap portion, so that localized strong near-field light is generated in the gap portion (bow-tie antenna method).
Meanwhile, a tip type probe has been studied in recent years as a recording and reproducing probe in an information recording apparatus. With an increase of a capacity of a hard disc or the like in a computer device, an information recording density within a single recording surface is increasing. For example, it is necessary to increase a surface recording density in order to increase a recording capacity per unit area of a magnetic disc. However, a recording area occupied by information per bit on a recording medium becomes smaller as the recording density becomes higher. When the bit size becomes smaller, energy that 1-bit information has approximates to thermal energy at room temperature. This raises a problem of thermal demagnetization, such as an inversion or a loss of recorded information due to heat fluctuation or the like.
A generally used in-plane recording method is a method of recording magnetism so that the direction of magnetization is oriented in the in-plane direction of a recording medium. This method, however, readily causes a loss of recorded information or the like due to thermal demagnetization as described above. In order to eliminate such an inconvenience, shifting is taking place to a perpendicular recording method by which a magnetization signal is recorded in a direction perpendicular to a recording medium. This method is a method of recording magnetic information by a principle to bring a single magnetic pole close to a recording medium. According to this method, the recording magnetic field is oriented in a direction substantially perpendicular to the recording film. It is easy for information recorded with a perpendicular magnetic field to keep stability in terms of energy because the N pole and the S pole hardly form a loop within the plane of the recording film. The perpendicular recording method is therefore more resistant to thermal demagnetization than the in-plane recording method.
Recording media in recent years, however, are required to have a further higher density to meet a need, such as performing recording and reproduction of a larger volume of information at a higher density. To this end, in order to minimize influences from one magnetic domain to adjacent magnetic domain and vice versa and heat fluctuation, media having a high coercivity are being adopted as recording media. This makes it difficult even for the perpendicular recording method described above to record information into a recording medium.
In order to eliminate this inconvenience, there has been provided a hybrid magnetic recording method (near-field light assisted magnetic recording method) by which writing is carried out while a coercivity is lowered temporarily by locally heating a magnetic domain with near-field light. The hybrid magnetic recording method is a method that utilizes near-field light generated by an interaction between a microscopic region and an optical aperture made in a size not greater than the wavelength of light generated at the near-field optical head.
By utilizing the microscopic optical aperture exceeding the diffraction limit of light, that is, the near-field optical head having a near-field light generating element in this manner, it becomes possible to handle optical information in a region not greater than the wavelength of light that is found to be the limit of the optical system in the related art . The density of the recording bit can be thus increased to the extent exceeding that of the optical information recording and reproduction apparatus in the related art.
Various types are provided as the recording head of the hybrid magnetic recording method described above and one of them is a magnetic recording head configured to increase a recording density by reducing the size of a light spot. For example, there has been proposed a structure by which near-field light is generated by forming a metal thin film of a bow-tie shape on the head bottom surface and irradiating light perpendicularly from above the recording medium, so that near-field light is imposed on a region to which the magnetic field is strongly applied (Patent Document 4). With this near-field light assisted magnetic recording head, the near-field light generating element is a plane film of bow-tie shaped metal formed on the head bottom surface, and near-field light is generated in the gap at the center of the bow-tie by guiding light from a laser via an optical fiber or the like for the light to be reflected on a mirror and irradiated to the bow-tie. Further, because the bow-tie serves also as a magnetic recording element, a medium surface region heated by near-field light coincides with a region magnetized by the magnetic field. A microscopic spot of near-field light can be therefore made as minute as possible to the utmost limit. Hence, this recording head is suitable for high-density recording. Meanwhile, by making the bow-tie structure in a tip shape, not only can a strong recording magnetic field be generated locally while collecting light efficiently, but also the manufacturing method can be simpler. However, a technique of actually manufacturing the tip structure described above has not been put into practical use.    Patent Document 1: JP-A-2001-118543    Patent Document 2: JP-A-11-265520    Patent Document 3: JP-A-2002-221478    Patent Document 4: JP-A-2002-298302 (pp.4-6, FIG. 1)    Non-Patent Document 1: Technical Digest of 6th international conference on near-field optics and related techniques, the Netherlands, Aug. 27-31, 2000, p100